Method of purifying gases using rotatable plates having a solid reaction surface layer thereon

ABSTRACT

A method of and apparatus for purifying gases, especially industrial waste gases, according to which a solid surface layer adapted to adsorb impurifications is formed on rotatable discs of which successive portions during the rotation of the discs temporarily protrude from a liquid containing container. This layer, when being contacted by the gas to be purified, adsorbs the impurifications and harmful substances of the gas. the exhausted portion of the surface layer is replaced successively by a new surface layer portion formed by wetting the disc portions when the latter pass through the liquid in the container.

United States Patent [191 Filss Sept. 23, 1975 METHOD OF PURIFYING GASESUSING ROTATABLE PLATES HAVING A SOLID REACTION SURFACE LAYER Tl-IEREON[75] Inventor: Peter Filss, Julich, Germany [73] Assignee:Kernforschungsanlage Julich Gesellschaft mit beschrankter I-Iaftung,Julich, Germany [22] Filed: July 19, 1973 [21] Appl. No.: 380,619

[30] Foreign Application Priority Data July 25, 1972 Germany 2236389[52] U.S. Cl. 423/210; 55/68; 55/74; 4 55/387; 423/230; 423/244 [51]Int. Cl. B01D 53/00 [58] Field of Search 423/210, 230, 239, 244,423/247; 55/68, 74, 387

[56] References Cited UNITED STATES PATENTS Coughlin 423/244 X PrimaryExaminerJohn l-l. Mack Assistant Examiner-W. 1. Solomon Attorney, Agent,or Firm-Walter Becker ABSTRACT A method of and apparatus for purifyinggases, especially industrial waste gases, according to which a solidsurface layer adapted to adsorb impurifications is formed on rotatablediscs of which successive portions during the rotation of the discstemporarily protrude from a liquid containing container. This layer,when being contacted by the gas to be purified, adsorbs theimpurifications and harmful substances of the gas. The exhausted portionof the surface layer is replaced successively by a new surface layerportion formed by wetting the disc portions when the latter pass throughthe liquid in the container.

7 Claims, 3 Drawing Figures US Patent Sept. 23,1975 Sheet 1 of23,907,967

US Patent Sept. 23,1975 Sheet 2 of2 3,907,967

1 1 METHOD or PURIFYING cAsEsiis Nc "1" ROTA'IABLE PLATES nxvmc'xsotm.REACTION SURFACE LAYER 'THLE REON The present inventioii relates toaimethod for purifying gases, especially industrial waste gases,according to which the gases are passed between plates above the liquidlevel, which plates rotate aboutan axis and immerge in a liquid by whichthey are wetted, the plates being spaced from each other by adistance ofa few millimeters. The particles forming the impurifications areadsorbed by the wetted surface. The present invention also concerns adevice for practicing this method.

A purification of industrial waste gases prior to their emission intothe atmosphereis necessary because such waste gases generally containvarious impurifications and harmful substances. For separating theimpurifications from the waste gases, numerous methods and devices havebecome known. The steps employed in this connection depend on therespective chemical properties and the degree of dispersion of theimpurities to be separated. As far as the separation ofmoleculardisperse harmful substances and impurifications of gases areinvolved, in particular wet purification methods have been employed sofar. In this connection, the gases to be purified are cooled andmoistened. This has the drawback that additional steps are necessary toimpart upon the gases the buoyancy necessary for their emission into theatmosphere. Another drawback consists in the fact that the gases arecharged with moisture and aerosols as it generally occurs when liquidwashers are employed for the wet treatment which affects the environmentin an undesirable manner. It is furthermore known to free carbon dioxidecontaining gases from volatile iron compounds by passing the gases at anincreased temperature over suitable. solid materials, such as lime,barium oxide, or the like. This method is FIG. 2 sh ows a front view ofthedevice of FIG. l, but with additional auxiliary devices. I

l f FIG. 3 is a side view of the device of FIG. 1, partly shown insection.

The method according to the present invention is characterizedin that onthe respective portion of the plates which is located above the liquidlevel there is formed a solid surface layer which adsorbs the impuriti-7 are removed, and the plates are again wetted. The imapplicable onlyfor the just mentioned purpose and has 7 the drawback that theregeneration of the employed adsorbing material has to be effected in adiscontinuous manner.

The prior art furthermore comprises methods for precipitating usefulsubstances or other admixtures from flue gases, according to which thegases are passed along discs which partly immerge in water or a chemicalliquid and which rotate at such low speed that they will remaincontinuously wetted with liquid. With this method, the particlessuspended in the gases are to adhere to the discs. This method, however,has the drawback that it remained limited to the employment of liquidadsorbing means. 1

It is, therefore, an object of the present invention to provide a methodand device which will make it possible safely to separateimpurifications and harmful substances from gases, especially industrialwaste gases, by binding such impurifications and harmful substances byreaction and adsorption to solid material-surface layers while it willbe assured that the separation can be carried out by a continuousregeneration of the solid material-surface layer without interruption.

These and other objects and advantages of the invention will appear moreclearly from the following specification in connection with theaccompanying drawings, in which: I

FIG. 1 is a perspective illustrationof a device accord ing to theinvention.

purifications and harmful substances contained in the gases are whencontacting the surface layer formed on the discs bound to this surfacelayer, while the surface layer, due to the adsorption or reaction withthe particles contained in the gases, is being transformed andexhausted. The exhausted layer can in the liquid normally be easilyremoved, but in difficult instances it can be removed by means ofbrushes, scrapers, and the like. Subsequently the plates are wetted witha fresh solution. From the thus created liquid film, a new solid surfacelayer will form due to drying. For forming the surface layer,expediently water soluble compounds are selected which bind thesubstances contained in the gases to the solidsurface layer formed onthe plates by the wetting. Thus, the liquid must be such that also thesubstances formed during the reaction of the impurifications and harmfulsubstances with the surface layer can be removed. In this way it will beassured that on the plates, following a further rotation through theliquid bath, the new film and the surface layer suited for theadsorption and, as the case may be, for the intended reaction will beformed.

As far as necessary, the plates are heated or cooled fully or partly.This will bring about that the intended solid surface layer will quicklyform after the plates emerge from the liquid. Furthermore, it will beassured that the method according to the invention is carried out at thetemperature most favorable for the respective type of purification. Forpracticing the method according to the invention, it is advantageousthat the liquid contains substances which during the evaporation or thereaction due to the adsorption of the impurifications on the surface"layer will form a gel with a structure rich in pores or a'frame-likestructure. As a result thereof, the effective surface of the adsorbingsurface layer and/or the surface layer reacting with the substancescontained in the gases will be enlarged.

A very advantageous device for practicing the method according to thepresent invention consists in that the plates are of circular shape andare firmly coaxially arranged on a hollow tube which is adapted in anyconvenient manner to be heated or cooled. As a result thereof, as far asthis may be expedient, the plates can be heated or cooled in a simplemanner. The continuous regeneration of the exhausted surface layer iseffected by slowly turning the hollow tube and the plates. The devicefor practicing the method according to the invention is particularlyeffective when the upper portion of the housing extends with slight playover that part of the plates which projects out of the liquid level. Ithas furthermore proved advantageous to make the diameter of the hollowtube larger than one third of the outer diameter of the plates. To makethe surface of the plates as large as possible, it is expedient toroughen the surface of the plates in any known manner mechanically or byetching. Another advantageous step for forming the surface layer on theplates consists in that on the plates there are arranged felt layerscomprising metal wires or thin layers of a known solid material having alarge surface, or that the plates have a regular or irregular profilewhich enlarges the surface.

If the load exerted on the hollow tube by the plates is so great that anundesired bending of the hollow tube occurs, supporting rollers arerotatably arranged in the housing for supporting the hollow tube and theplates connected thereto.

A preferred embodiment of the device according to the present inventionconsists in that the hollow tube projects partially beyond the liquidlevel and that above the liquid level on both sides of the hollow tubein the gap formed by the housing and the hollow tube there are providedcomb-shaped strips which extend into the vicinity of the hollow tube andengage the spaces between the plates. These comb-shaped strips extendparallel to the longitudinal axis of the hollow tube and are connectedto the inner wall of the housing. In order to realize a fast removal ofthe layer forming on the plates from the plates, brushes or scrapers maybe arranged within the liquid bath which are in contact with thesurfaces of the plates. Instead of this arrangement, it is also possiblefor removing the surface layer after the latter is loaded to arrangewithin the liquid bath an ultrasound device known per se. It isexpedient that the feeding of the gas to be purified and the withdrawalof the purified gas is effected through connections which are arrangedon opposite sides of the housing. In this way it will be brought aboutthat the gas passes in radial and azimuthal direction through the spacesdefined by the plates above the liquid level. If the liquid in thecontainer is replaced and withdrawn continuously, it is expedient thatwith a continuous feeding-in and withdrawal of the liquid the feeding iseffected at that point of the housing where the freshly wetted platesemerge from the liquid, whereas the withdrawal should be effected on theopposite side of the housing.

The method and device according to the invention are well suited forseparating molecular disperse impurifications and harmful substancesfrom air or CO containing waste gases, such as 1,, and are particularlywell suited for substances with typical acid character, such as HCl and80,.

Referring now to the drawings in detail, the arrangement shown thereincomprises a housing 1 in which on a hollow tube 2 rotatably joumalled inthe housing there are arranged a plurality of plates 3 which arerotatable about their axes and are spaced from each other by a distanceof a few millimeters. Tube 2 and plates 3 form a rigid unit with eachother. The lower portion of the container-shaped housing 1 is adapted toreceive and contain a liquid bath 4. The plates 3 immerge into thisliquid bath. To this end, housing 1 is widened in the manner of a bottombased vessel. The height of the liquid bath 4 is expediently so selectedthat the hollow tube 2 divides the level of the liquid bath 4 into tworanges. The liquid bath 4 is chemically so composed that the layer 5,which during the rotation of the plates 3 is formed on the plates withinthe region above the liquid level 11 by wetting and drying, is suitablefor the adsorption of and/or, as the case may be, for the reaction withthe substances which are contained in the gas to be purified and whichare to be separated. As will be evident from the drawing, the upperportion of housing 1 extends with slight play around the plates 3. Ifthe gas to be purified flows from the connection 6 arranged laterally onthe housing 1 into the space above the liquid level 11, the gas willflow through the spaces between the plates 3 and will leave the housing1 through the connection 7. If desired, it may be expedient, in order torealize as uniform a distribution as possible of the incoming gas whenflowing into the housing 1, to provide guiding plates in the feedingconnection 6. When the gas passes through the spaces between the plates3, the undesired components contained in the gas are adsorbed by thesurface layer 5 which during the rotation of plates 3 is formed bydrying of the wetting liquid. During the formation of the solid layers5, which is effected in conformity with the method according to theinvention on the surface of plates 3, the temperature of the gases to bepurified which is frequently above room temperature, will be takenadvantage of. If this should not suffice or if high temperatures favorthe desired reaction, a heating device 8, for instance gas burners, maybe provided in the hollow tube 2. Instead, also an electric or hot steamor hot air heating device may be provided. The speed of rotation ofplates 3 is furthermore so selected that the plates will remain moistonly in a relatively small range above the liquid level 11 and will bedried in a short time. To prevent a simultaneous heating up of theliquid bath 4, it may be expedient to provide cooling coils 9 within thebath. In order to realize both, the heating up of the plates 3 in therespective range of plates 3 above the liquid level 11 and also acooling of the liquid bath, it is expedient to select the diameter ofthe hollow tube 2 relatively great in comparison to the outer diameterof the plates 3.

To prevent a strong evaporation of the liquid into the gas which flowsabove the hollow tube 2, comb-like strips 10 are on both sides of thehollow tube 2 and above the liquid level 11 connected to the inner wallof the housing 1 and extend parallel to the axis of the hollow tube 2.As will be evident from the drawings, the plates 3 extend between thestrips 10.

The rotation of the plates 3 may be effected in a direction which isopposite to the direction of flow of the incoming gas. This is indicatedby the arrows in FIG. 1. The rotary movement of plates 3 may, however,if this should be expedient, also be effected in the same direction asthe direction of flow of the incoming gas.

As not shown in the drawings, the plates 3 may, if necessary, forenlarging their surface, be lined with a thin layer of a material havinga large surface, such as pumice or the like. Instead, the liquid bathmay have added thereto a substance which during the evaporation orduring the purification process forms a gel with a large surface or aframe-structure. To this end, for instance, waterglass may be used fromwhich during a reaction with acid gases the large surfaceframe-structure of silicic acid is formed. Another possibility toenlarge the surface of the plates 3 consists in mechanically or byetching roughening the surface of the plates. If considered necessary,the plates 3 may entirely or partly have a corrugated or edged profile.In order to make sure that the solid material adsorption layer formed onthe surfaces of the plates will be very carefully and quickly washedoff, there are within the liquid bath 4 provided brushes 12 (FIG. 2,),which on theinside of the liquid bath 4 are in contact-with both sidesof the plates. Instead thereof or in addition theret it is also uid, thefeeding line 15 for the liquid is preferably provided on that side ofthe housing on which the plates 3. are through the liquid bath 4 rotatedto the outside.

while the discharge conduit 16 is provided on-that side of the housingon which the exhausted-orused-up layer is removed from the plates 3. Thedriveand the mount- I ing of the hollow tube 2' are arranged outside thehousing 1 (not shown in the drawings); Y

Relative HCI Cl1- Relative HCl con- Qte'nt prior to the tent after thegas of the raw "gas gaspurification purification 'lz l/ll' l' l/lsoo 25l/h. 1. H350 -50.l/h l 1/25 llh I l I13 a f EXAMPLE 3 4 During thepurification of HCI-containing air under the'same conditions asin'Example 2, but with a bath liquid of waterglass diluted with water atthe ratio of l: 1 "(Merck Article No. 5621 the following values wereobtained:- v

By means of the device accordingto-the invention as described above, inwhich ten plates having a diameter of 90 mm and a thickness of 5mm arearranged on a! hollow tube having a diameter of 50 mm thespacing betweenthe plates being 5 mm -'-,"the following gas purifications have beeneffected. The't'eniperat'ure of the liquid bath was 30C, while thetemparature' between the plates amounted to 100C. Both temperatures weremeasured by means of mercury thermometers. Priorto practicing themethod, the entire'd evice was each: time cleaned by means of a washingsolution.

EXAMPLE 1 Iodine containing air was purified by means of the deviceaccording to the invention. The device contained a 10% Klsolution asliquid bath from which the adsorption layer formed. For producing theiodine containing air, first ordinary air was at room temperaturesaturated with iodine steam by air fiowing over iodine crystals. Thepartial pressure of the iodine in the added air amounted to 0.25 Torr.With the plates mounted on the hollow tube rotating at a speed of 8 rph,the following values were obtained:

Relative Iodine con- Relative iodine con- Flow velocity tent prior tothe tent after the gas of the raw gas gas purification purification l2l/h l l/ 100 25 l/h l l/lOO 50 Ill! 1 H 100 l/h l 114 250 llh 1 H2 Therelative iodine content was determined calorimetrically by discolorationof starch paper.

The uniform brown coloration of the bath liquid by l, in the region ofthe immersed plates indicates that the iodine adsorption and thus alsothe gas flow were distributed uniformly over the individual chambers ofthe plate packet.

EXAMPLE 2 HCI-containing air was purified by means of NaOH as bath andadsorbing substance. For producing HCI- containing air, first ordinaryair was charged with HCI by flowing over a 35% hydrochloric acid; at aflow velocity of l/h, the HCL partial pressure amounted to Torr. Therotational speed of the plates on the hollow tube amounted to 12 rph.The following values were obtained:

Relative HCI con- Relative HCI conl low velocity tool/ll l/20Theexhausted or used-up layer sealed off from. the

' plates inithefma nner of fish scales.

EXAMPLE 4" 3 SO -containing air was purified by means of a liquid bathwhich contained 100 g of NaOH per one liter of the bath. The SO-containing air had previously been prepared by passing air through apiston in which a diluted sulfuric acid dripped onto sodium sulfite. Ata flow velocity of 50 l/h, the partial pressure of the SO, amounted to 6Torr. At a speed of rotation of 12 rph, the following values wereobtained.

Relative 80, con- Relative SO, eon- The layer which detached itself fromthe plates had a character similar to that of the embodiment of Example3.

It is, of course, to be understood that the present invention is, by nomeans, limited to the specific showing in the drawings and to thespecific examples set forth in the specification, but also comprises anymodifications within the scope of the appended claims.

What I claim is:

l. A method of purifying gases, especially industrial waste gases, bymeans of rotatable plates axially spaced from each other by a fewmillimeters and partially immersed into a liquid for forming anadsorption layer on the plates wetted by said liquid for adsorbingimpurities from the gas to be purified, which includes in combinationthe steps of: employing as liquid an aqueous solution adapted on thoseportions of the rotatable plates which during the rotation thereof areabove the level of V the liquid to form a solid surface layer capable toadsorb impurities and harmful substances from the gas to be purifiedbetween the respective plate portions which during rotation of thelatter are above the level of the liquid, rotating the plates, formingthe solid surface layer, feeding impure gas between the plates, andremoving impurities and harmful substances adsorbed by said solidsurface layer from said plates and'replacing exhausted portions of saidlayer by a fresh forming solid layer by immersing the plate portionsinto said liquid, said solid surface layer being operable to chemicallyreact with and bind impurities and harmful substances in the gas to bepurified and passing between said plates.

2. A method in combination according to claim l',-in which as liquid anaqueous solution is employed-which contains a substance adapted whenreacting with said surface layer to bring about a generation of agelwith a frame structure.

3. A method in combination according to claim 1, which includes the stepof changing the temperature of at least a portion of said platesfor thepurpose of formtatable driven plates which during the rotation thereofare above the level of the liquid to form by evaporation of the liquid asolid surface layer capable to adsorb and to chemically react impuritiesand harmful substances .-mersing the plate portions into said liquid.

ing the solid layer on the plate portion above-the liquid.

4. A method of purifying gases, especially industrial waste gases bymeansof rotatable driven plates axially spaced from each other by a fewmillimeters and par- 'cally reacting impurities from the gas to bepurified,

which includes the steps of: employing as liquid an aqueous solutionadapted on those portions of the ro- 5. A method according to claim 4,which includes the step of changing the temperature of said plates toincrease the speed of forming said solid surface layer and .the reactionof said solid surface layer with said impurities.

16. A method'according to claim 4, in which as liquid an aqueoussolution is employed which contains a substance adapted when subjectedto evaporation to bring about the generation of a gel with a structurerich in pores.

7. A method according to claim 4, in which as liquid an aqueous solutionis employed which contains a substance adapted for the generation of aframe structure during reaction of said impurities of the gases withsaid solid surface layer. i

1. A METHOD OF PURIFYING GASES, ESPECIALLY INDUSTRIAL WASTE GASES, BYMEANS OF ROTABLE PLATES AXIALLY SPACED FROM EACH OTHER BY A FEWMILLIMETERS AND PATIALLY IMMERSED INTO A LIQUID FOR FORMING ABSORPTIONLAYER ON THE PLATES WETTED BY SAID LIQUID FOR ABSORBING IMPURITIES FROMTHE GASES TO BE PURIFIED, WHICH INCLUDES IN COMBINATION THE STEPS OF:EMPLOYING AS LIQUID AN AQUEOUS SOLUTION ADPTED ON THOSE PORTIONS OF THEROTATABLE PLATES WHICH DURING THE ROTATION THEREOF ARE ABOVE THE LEVELOF THE LIQUID TO FORM A SOLID SURFACE LAYER CAPABLE TO ABSORB IMPURITIESAND HARMFUL SUBSTANCES FROM THE GAS TO BE PURIFIED BETWEEN THERESPECTIVE PLATE PORTIONS WHCH DURING ROTATION OF THE LATTER ARE ABOVETHE LEVEL OF THE LIQUID, ROTATI NG THE PLATES, FORMING THE SOLID SURFACELAYER, FEEDING IMPURE GAS BETWEEN THE PLATES, AND REMOVING IMPURITIESAND HARMFUL SUBSTANCES ABSORBED BY SAID SOLID SURFACE LAYER FROM SAIDPLATES AND REPLACING EXHAUSTED PORTIONS OF SAID LAYER BY A FRESH
 2. Amethod in combination according to claim 1, in which as liquid anaqueous solution is employed which contains a substance adapted whenreacting with said surface layer to bring about a generation of a gelwith a frame structure.
 3. A method in combination according to claim 1,which includes the step of changing the temperature of at least aportion of said plates for the purpose of forming the solid layer on theplate portion above the liquid.
 4. A method of purifying gases,especially industrial waste gases by means of rotatable driven platesaxially spaced from each other by a few millimeters and partiallyimmersed into a liquid for forming a layer on the plates wetted by saidliquid for adsorbing and chemically reacting impurities from the gas tobe purified, which includes the steps of: employing as liquid an aqueoussolution adapted on those portions of the rotatable driven plates whichduring the rotation thereof are above the level of the liquid to form byevaporation of the liquid a solid surface layer capable to adsorb and tochemically react impurities and harmful substances from the gas to bepurified, forming a solid surface layer above the level of the liquid,passing the gas to be purified between the respective plate portionswhich during rotation of the latter are above the level of the liquid,and removing impurities and harmful substances chemically fixed by saidsolid surface layer from said rotatable driven plates and replacingexhausted portions of said layer by a fresh forming solid layer byimmersing the plate portions into said liquid.
 5. A method according toclaim 4, which includes the step of changing the temperature of saidplates to increase the speed of forming said solid surface layer and thereaction of said solid surface layer with said impurities.
 6. A methodaccording to claim 4, in which as liquid an aqueous solution is employedwhich contains a substance adapted when subjected to evaporation tobring about the generation of a gel with a structure rich in pores.
 7. Amethod according to claim 4, in which as liquid an aqueous solution isemployed which contains a substance adapted for the generation of aframe structure duRing reaction of said impurities of the gases withsaid solid surface layer.